Increasing the X axis precision while using times

Hello, I am trying to plot a graph that takes place over a set of times from 00:00 on one day to 18:00 the next day. My code is:

r8s = readmatrix('hhh.csv');
start = datenum('00:00')
finish = datenum('18:37')

x = linspace(start, finish, 2558);
figure(1) 
plot(x, (r8s(:,9) - r8s(:,4)))
yline(0)
dateformat=15
datetick('x', dateformat)
grid on
xlabel('Time UTC')

Which gives the times in three-hour increments. I would like them in 15 minute increments if possible, but have no idea how to achieve this, and trying to manually manipulate the Xticks has not worked for me. Any ideas would be appreciated.

Answer 1

[Adam Danz]

Give this a shot.

I've added/changed 3 lines (see comments) and removed two lines.

Avoid using datenum and use datetime instead.

r8s = readmatrix('hhh.csv');
start = datetime('00:00','format', 'HH:mm');  % Use datetime
finish = datetime('18:37','format','HH:mm');  % Use datetime
x = linspace(start, finish, 2558);
figure(1) 
plot(x, (r8s(:,9) - r8s(:,4)))
yline(0)
grid on
xlabel('Time UTC')
set(gca, 'xtick', start : minutes(15):finish) % set ticks at 15 min intervals

But that's going to give you 75 ticks! So you might need to increase the interval or rotate the ticks: xtickangle(90).

[Noob Tubem]

Thank you! This worked perfectly (although I decided to drop my precision to an hour)

[Adam Danz]

Good call.

[Steven Lord]

Rather than using linspace to create x, I'd use colon. I'll use a smaller interval so I can actually show the result.

start = datetime('00:00', 'Format', 'HH:mm');
finish = datetime('01:37', 'Format', 'HH:mm');
x = start:minutes(15):finish

x = 1×7 datetime array
   00:00   00:15   00:30   00:45   01:00   01:15   01:30

There is one "gotcha" here in that the last element of x is not equal to finish. But is that desirable if finish is not exactly a multiple of the interval away from start?

if x(end) ~= finish
    x(end+1) = finish;
end
disp(x)

   00:00   00:15   00:30   00:45   01:00   01:15   01:30   01:37

plot(x, (1:numel(x)).^2, 'o-')

And if you don't need the date part of the datetime use a duration array instead.